The two "sales are not a problem. Open a new 6252 for the second buyer. Treat the original sale as below.
Repossession
If you repossess your property after making an installment sale, you must figure the following amounts.
Your gain (or loss) on the repossession.
Your basis in the repossessed property.
The rules for figuring these amounts depend on the kind of property you repossess. The rules for repossessions of personal property differ from those for real property. Special rules may apply if you repossess property that was your main home before the sale. See Regulations section 1.1038-2 for further information.
The repossession rules apply whether or not title to the property was ever transferred to the buyer. It doesn’t matter how you repossess the property, whether you foreclose or the buyer voluntarily surrenders the property to you. However, it isn’t a repossession if the buyer puts the property up for sale and you repurchase it.
For the repossession rules to apply, the repossession must at least partially discharge (satisfy) the buyer's installment obligation to you. The discharged obligation must be secured by the property you repossess. This requirement is met if the property is auctioned off after you foreclose and you apply the installment obligation to your bid price at the auction.
Reporting the repossession. You report gain or loss from a repossession on the same form you used to report the original sale. If you reported the sale on Form 4797, use it to report the gain or loss on the repossession.
<a rel="nofollow" target="_blank" href="
https://www.irs.gov/publications/p537">https://www.irs.gov/publications/p537</a>
